Path constraint switching and timing
I recommend you for using bake animation. The follow step :


First, you set the object to follow the path by adding it on the "Add Object Constraint" 
Then, you set the thing, like control the speed (actually just control the frame), direction etc
Bake animation
The switch to another path using dope sheet.


How to bake steps you could check this link :
How can a path animation be used as an action in the game engine?

Hope this help :)